The present invention relates generally to autonomous detection and alerting to motion, such as ice flow in a river. More particularly, it provides a sealed, inexpensive, fully integrated, remote, early-warning system for continuous detection and early warning of river ice flow hazards. It may be solar powered with battery backup, with an option for at least one battery to be solar rechargeable.
Alerting to a waterway""s ice motion during winter frazil ice flow and spring ice breakup is important. The ability to detect river ice sheet and rubble motion can provide early warning to communities and facilities down-river, helping prevent the loss of life, flooding, and infrastructure damage often associated with massive ice rubble flows. Unfortunately, this information is often not available at all, and, when available, it may be hazardous, difficult, time consuming, and expensive to obtain.
Currently, there are three methods employed to detect movement of an ice sheet. The first, visual observation, requires the constant attention of a human observer. This method is particularly inefficient, as it can be hindered by darkness or by low-visibility weather conditions.
Video monitoring of the ice sheet is similarly limited by the short periods of daylight in northern latitudes in the winter, weather conditions and the need for the presence of both equipment and operator at the time the ice sheet moves. Video monitoring has the further disadvantage of requiring tedious, frame-by-frame motion analysis and the inclusion of known benchmarks in the video frame from which to measure or detect motion.
A third method uses a frangible wire embedded in the river ice to detect movement. When the ice moves, the wire breaks, opening a circuit and triggering an alarm. However, deploying the wire across the ice sheet or rubble field may be extremely hazardous. Furthermore, this primitive method provides only a one-time indication of movement, thereby necessitating repeated hazardous deployments in order to reset the alarm.
A number of patents utilizing the Doppler effect at various frequencies for motion detection and other applications have been issued. Each is distinguishable from the instant invention.
U.S. Pat. No. 5,585,799, Microwave Doppler Radar System for Detection and Kinematic Measurements of River Ice, to Yankielun and Ferrick, Dec. 17, 1996, incorporated herein by reference, teaches a Doppler ice motion detection system for measuring the velocity of an ice sheet. However, the device disclosed in the ""799 patent is not capable of autonomous operation, and is thus not well suited to long-term monitoring of an ice sheet. Further, it employs expensive components, making it relatively less suitable for widespread use in simple detection of the dynamics of ice sheet motion. Rather, it is best used when seeking highly accurate scientific data during a relatively short-term movement of an ice sheet.
U.S. Pat. No. 6,333,691 B1, Motion Detector, to Janus, Dec. 25, 2001, employs the Doppler phenomena to detect motion by comparing phase or amplitude changes as determined from separate transmit and receive antennas. It also permits operation of the system through otherwise interfering materials via judicious selection of the frequency of operation.
U.S. Pat. No. 6,324,912 B1, Flaw Detection System Using Acoustic Doppler Effect, to Wooh, Dec. 4, 2001, employs an acoustic transducer and makes use of the Doppler effect at acoustic frequencies to detect flaws in material under inspection. A particular application is detecting flaws in railroad tracks in real time during operation of a rail riding vehicle.
U.S. Pat. No. 5,587,713, Radar Transmitter/Receivers, to Pfizenmaier, et al., Dec. 24, 1996, provides an RF transmit-receive capacity on a single PC board using a ratrace device for inputting RF energy to a mixer from the transmitter and the transmit-receive antenna.
U.S. Pat. No. 5,966,090, Differential Pulse Radar Motion Sensor, to McEwan, Oct. 12, 1999, details a pulsed Doppler system for overcoming inherent disadvantages of CW Doppler systems. It yields a constant response versus distance to motion within at least one gated range. It may also provide target direction using a quadrature receive channel.
U.S. Pat. No. 6,380,882 B1, Motion Detector Based on the Doppler Principle, to Hegnauer, Apr. 30, 2002, uses two separate RF frequencies to detect motion within a room, comparing the phase difference between these two to detect motion. The design also incorporates suppression circuitry to deal with multi-path interference.
U.S. Pat. No. 5,977,874, Relating to Motion Detection Units, to Konstandelos, Nov. 2, 1999, provides an RF transceiver on 2 separate PC boards, one for the electronics and the other for the transmit-receive antenna. The two boards are separated by a common ground plane in a preferred embodiment. The system employs the Doppler phenomenon to detect motion and is of a smaller size than previous designs.
U.S. Pat. No. 5,262,783, Motion Detector Unit, to Philpott et al., Nov. 16, 1993, is similar to the ""874 patent in that it consists of two PC boards, an antenna board and the electronics board. However, the boards have no electrical connection therebetween, relying on two slots resonant at the oscillator""s fundamental frequency to couple the antenna to the transceiver. Feed striplines on the boards lie orthogonal to the slots, suppressing the oscillator""s 2nd harmonic frequency.
U.S. Pat. No. 5,497,163, Doppler Radar Module Using Micro-Stripline Technology, to Lohninger et al., Mar. 5, 1996, provides a transceiver and mixer-antenna configuration for utilizing the Doppler effect. It is mounted on a compact multi-layer motherboard, enclosed in a housing of electrically conductive material.
U.S. Pat. No. 5,684,458, Microwave Sensor with Adjustable Sampling Frequency Based on Environmental Conditions, to Calvarese, Nov. 4, 1997, provides an adjustable motion detector using the Doppler effect. For adverse environmental conditions, such as thermal noise, that exceed a pre-specified threshold, a processor incorporated in the system changes the sampling frequency.
Thus, needed is an autonomous, reliable and inexpensive detection and warning device that also eliminates exposure of personnel to environmental hazards when installing or maintaining it. Applications in nature include warning of flash floods, mudslides, tidal waves, tsunamis, land slides (falling rocks), and snow avalanches. In industry, applications include landslides in open-pit mining operations, instabilities in below ground mines, and security operations including perimeter or border monitoring and intrusion sensing.
A preferred embodiment of the present invention is a compact and relatively inexpensive motion detection and alerting system implemented in a single, environmentally secure and benign package. Further it is capable of autonomous continuous operation, if necessary. It operates autonomously detecting motion within a pre-specified velocity range. In general its components include a transceiver sub-assembly and a signal processing sub-assembly.
The transceiver sub-assembly propagates electromagnetic energy as a transmitted signal in a pre-specified pattern and direction to illuminate a non-smooth surface. It receives at least some energy reflected therefrom as a reflected signal and provides a reference signal.
The signal processing sub-assembly communicates with the transceiver sub-assembly, determining the difference in frequency between a reference sample of the transmitted signal and the reflected signal. Further processing establishes the existence of a pre-specified range of Doppler frequencies that may be correlated to motion of the non-smooth surface, e.g., an ice sheet. Using a decision algorithm to identify non-transient velocities within a pre-specified velocity range enables alerting via a cellular telephone.
Components of the transceiver sub-assembly include a transceiver, a T-connector between the transceiver and an antenna, an impedance matching device between the T-connector and the antenna, and a signal mixer connected to the xe2x80x9cbasexe2x80x9d of the T-connector. The signal mixer receives signal inputs from the transceiver and the antenna via the T-connector and outputs signal products, to include a signal at a Doppler frequency as appropriate.
In a preferred embodiment, the system is mounted on a single printed circuit (PC) board. The PC board includes a CW microwave source having an average output power between 10 and 20 dBm, the T-connector, an impedance matching transformer, a strip line beam antenna and a single-end signal mixer.
The antenna may be any of: a stripline antenna, a stripline beam antenna, a Yagi stripline beam antenna, a log periodic array (LPA) stripline beam antenna, a wire element beam antenna, a tubular element beam antenna, a microwave horn antenna, a microwave dish antenna, and any combination thereof. However, for the system to be fitted to a preferred embodiment, i.e., a single PC board, only the stripline antennas may be used. Preferably, the antenna offers forward gain of approximately at least 10 dB and antenna main lobe dimensions of approximately 60xc2x0 or less.
Preferably, the processing sub-assembly includes analog circuitry connected to the transceiver sub-assembly through a mixer. This analog circuitry conditions output signals from the mixer for digital processing. Digital circuitry receives conditioned output signals from the analog circuitry, converts it to digital format, and employs a decision algorithm for determining movement of the non-smooth surface. A communications device receives output from the digital circuitry that indicates target movement and provides the necessary alert.
In a preferred embodiment, the analog circuitry includes a first amplifier for amplifying the signal products from the mixer, a bandpass filter that passes only those Doppler frequencies that correlate to the pre-specified velocity range, a second amplifier for amplifying the output of the bandpass filter, and a Schmitt trigger for final conditioning of the output from the second amplifier.
The digital circuitry includes an analog-to-digital (A/D) converter for converting the output of the Schmitt trigger, a digital signal processor (DSP), and a communications device including an autodialer, a cellular phone and a cellular phone antenna. The DSP implements a decision algorithm and an optional power management function. Preferably, all system components noted above are enclosed within a weatherproof enclosure.
Preferably, the system includes it own power source installed on the single PC board. The power source may include a solar panel augmenting a rechargeable battery. Further, a preferred embodiment may include its own mounting bracket. In addition to the system itself, a unique method of implementing a motion detection capability is provided.
Provided is a method for detecting and alerting to the movement of an irregular or non-smooth target surface. It comprises mounting a motion detection and alerting system of the present invention at a pre-selected look angle in azimuth and elevation; providing power to the system; illuminating at least part of a target surface with a signal containing electromagnetic energy; receiving energy reflected from the target surface as a result; processing the reflected energy together with a reference signal provided from the transceiver to produce a difference frequency signal representing the difference in frequency between the reference signal and the reflected energy; establishing a value of the difference frequency signal, such that a non-zero value indicates motion that may be of a pre-specified type; processing any non-zero value difference signals by implementing a decision algorithm to minimize false alarms; and using the output of the decision algorithm, providing notification of any occurrence of the pre-specified type of motion. The notification, at least in part, may comprise placing a telephone call automatically. Establishing the value of the difference frequency signal may further comprise introducing a pre-specified delay period prior to sending the notification.
Further, the method may include selectively powering the components based on system demand, i.e., power management. It may also include mounting the system such that the antenna is oriented in respect to the target surface at an offset angle less than approximately 60xc2x0 both laterally and in elevation and more preferably at an offset angle between approximately 0xc2x0 and 30xc2x0 both laterally and in elevation. Should one desire to use the system for capturing precise measures of movement velocity, one may employ an inclinometer to achieve an accuracy of at least xc2x11.0xc2x0 in orienting said system.
In a preferred embodiment, an autonomous ice sheet and rubble motion detecting and alerting system is provided in which components of the system as described above are mounted on a single printed circuit (PC) board. The existence of a pre-specified range of Doppler frequencies is correlated to an expected velocity of motion representative of the ice sheet and rubble.
Any embodiment of the system may be powered by any of a number of sources including a source remote from its location and a backup source.
In one application, a preferred embodiment of the present invention is mounted at a location proximate a target surface to be observed such as an ice sheet or rubble (debris) field. The target may be remote from the responsible authority who may be mobile, thus a wireless communications device is provided in a preferred embodiment. A reference signal, ƒsource, is transmitted from the antenna towards the target surface. Resultant reflected radiation, i.e., the xe2x80x9cbackscatteredxe2x80x9d portion, is mixed with a portion of the transmitted signal sampled for that purpose. This mixing produces a difference, or Doppler, frequency ƒDOP, which is then processed to establish movement of the target surface.
Digital circuitry implementing a decision algorithm establishes movement of the target surface, including movement on the target surface. Using the decision algorithm, the difference frequency is established to be non-zero for a sufficient amount of time to rule out transient motion, e.g., a hiker crossing the transceiver""s field of vision. Upon such determination, the system sends a notification, preferably over a wireless communications device, to a responsible authority at a remote location.
Further advantages of the present invention will be apparent from the description below with reference to the accompanying drawings, in which like numbers indicate like elements.